A machine tool with a spindle device having a mist generating member in a center hole of a spindle driven for rotation has been disclosed in a prior art reference, for example, Japanese Patent No. 2687110 and Japanese Patent Provisional Publication No. 235641 of 1999. As shown therein, coolant mists spouted from a non-rotatable mist outlet member of the mist generating member escape from a tip opening of a tool through a center hole of a tool holder before the mist outlet member.
In this machine tool, the diameter of a mist passage from the front end of the mist outlet member to the rear end of the tool changes in size comparatively greatly, and the mist passage part with comparatively large diameter is rotated together with the spindle. Therefore, coolant mists are liquefied in the mist passage over permissible limits by big pressure change, speed change and centrifugal force, and come not to flow out of the tip opening of the tool constantly. Accordingly, the quality of machining drops and unusual wear of a tool is caused.
The present invention aims to provide a spindle device of a machine tool that can settle these problems.